Settings > Apps and Notifications > Advanced > Default Apps doesn't actually seem to have a music setting at all.

If I open the assistant and say "open MediaMonkey", it does open the app. If I say "play [song name] with MediaMonkey" it searches Google Play Music for "[song name] with mediamonkey". If I say "play music" it asks me to choose from a list of apps which does not include MMA.

I can't find anything saying support has been removed. I'm out of ideas and search engine results.

Hi,
MediaMonkey didn't get/passed Google Assistant testing, we are investigating better integration and only recently Google published custom triggers for external apps. I have same issue on Nexus Player where MediaMonkey do not get recognized as MediaPlayer, but if MMA is open then basic voice commands work.